In recent years, there has been focused on a hybrid vehicle as one type of vehicle of environment-friendly automobiles. The hybrid vehicle has driving sources including an internal combustion engine (hereinafter referred to as “engine”) powered by fuel such as, for example, gasoline, and an electric motor (hereinafter referred to as “motor”) powered by electric power from a battery.
There has already been developed an above mentioned type of a hybrid vehicle mounting a vehicle control apparatus (see, for example, Patent Document 1). The vehicle control apparatus includes an engine, a motor, a clutch, and a control unit. The clutch is adapted to connect and disconnect between the engine and the motor. To start the engine, the vehicle control apparatus is designed to engage the clutch and to drive the engine to start rotating through the engaged clutch by the motor.
As shown in FIG. 5, at a time T0 under the state that the engine is stopped while the hybrid vehicle is stopped, the control unit controls the motor to start rotating in order to drive the engine to start rotating in response to an engine start request flag turned “ON”. After that, the control unit controls the motor to increase a motor rotational speed NM. After the motor rotational speed NM reaches a target rotational speed capable of starting the engine at a time T1, the control unit controls a clutch to take an engaging state from a disengaging state by turning a clutch flag “ON”.
To start the engine, the motor is required a load torque increased to a level capable of driving the engine to start rotating through the clutch taken the engaging state. The control unit is therefore configured to calculate, before the clutch takes the engaging state, the load torque to be increased for driving the engine to start rotating and set the calculated load torque as a compensating torque TM of the motor. In addition, the control unit is configured to control the motor to increase an output torque by the compensating torque TM at the time of the clutch taking the engaging state.
As shown in FIG. 5, a clutch torque TC is increased in response to changing the clutch to take the engaging state from the disengaging state at the time T1. The control unit is configured to increase the compensating torque TM along the increase of the clutch torque TC keeping the compensating torque TM slightly less than the clutch torque TC.
The engine has a crankshaft driven by the motor through the clutch. In response to changing the clutch to take the engaging state from the disengaging state, a rotational speed of the crankshaft, i.e., an engine rotational speed NE is gradually increased. In case that the clutch is completely engaged at a time T2, the engine rotational speed NE is synchronized with the motor rotational speed NM at the target rotational speed. The engine is therefore driven to start rotating by the motor.